1. Field of the Invention
The present invention relates to a method of making an optical element and to the optical element. In particular, the present invention relates to a method of making an optical element whose effective permeability is artificially changed by including magnetic resonators and to the optical element.
2. Description of the Related Art
Metamaterials have been proposed in recent years. A metamaterial is a material including a medium and artificial structures. The artificial structures are made of a metal, a dielectric, or a magnetic substance and smaller than the wavelength of incident light. By including the artificial structures, the permittivity or the permeability of the metamaterials are artificially changed from that of the medium. For example, when a metamaterial is made so as to have a negative permittivity and a negative permeability, a negative refractive index can be realized. By using a negative refractive index, a new optical phenomenon, such as imaging beyond the diffraction limit (perfect lens), can be caused. By independently controlling the permittivity and the permeability, the impedance can be appropriately controlled, whereby perfect reflection and a structure having a reduced reflectivity can be realized. Moreover, by controlling the permittivity and the permeability, applications having new optical characteristics that do not exist in nature have been proposed.
Examples of the structures that enable artificial control of permeability include magnetic resonators such as split-ring resonators. The magnetic resonators change the permeability by resonating with the magnetic field component of an incident light wave. By including the magnetic resonators in an optical element, the effective permeability of the optical element can be changed. An optical element including the magnetic resonators is usually made by creating small structures made of a metal or the like by lithography such as electron beam lithography (Optics Letters, vol. 31, pp. 1259-1261, 2006). A method of depositing a metal by focusing a laser beam on a metallic complex ion dispersion that is dispersed in a medium has been proposed (Japanese Patent Laid-Open No. 2006-350232). In both of these methods, an upper surface of a substrate is processed so as to make a layer including magnetic resonators, and the layer is stacked so as to make an optical element 10 as illustrated in FIG. 11. Because the upper surface of a substrate 11 is processed, split rings that function as magnetic resonators 12 are disposed parallel to the substrate 11. Therefore, resonance directions 13 of the magnetic resonators 12 are perpendicular to the substrate 11.
In the existing optical element 10 illustrated in FIG. 11, in order to make the magnetic resonators 12 resonate with the magnetic field component of a light wave 14 that is incident on the optical element, it is necessary that the light wave 14 be incident in a direction parallel to the substrate 11, because the magnetic field component of the light wave 14 is perpendicular to the direction of incidence. Therefore, the existing optical element 10 has an incident surface 15 on a side of the substrate 11, which leads to a problem in that the cross-sectional area of incidence of the optical element 10 is small. The use of an optical element having a small cross-sectional area of incidence is limited to a planar waveguide or the like. Making an optical element having a large cross-sectional area of incidence is difficult, because it is necessary to increase the number of stacks. For example, if the thickness of one stack is 1 μm, about 1000 stacks are necessary to obtain an incident surface having a thickness of 1 mm, and about 10000 stacks are necessary to obtain an incident surface having a thickness of 1 cm.